How to convert images from logarithmic space to linear?
If you intend to transform a log encoded image to scene referred linear, you need to be certain of the following characteristics:


The log encoding format of your source footage. There are many different log encoding formats, and to achieve a proper transform, the exact log encoding, with variables, must be known.
The source footage colour primaries. The source is encoded with specific colour primaries that must be known.
The destination colour primaries. These must be known to transform to your reference correctly. Blender's default configuration reference space assumes BT.709 primaries, for example.
The destination transfer characteristics. In the case of default Blender, the reference space in the compositor is scene referred linear.


Once you know these details, the proper transforms can be added to the OpenColorIO configuration, and your data can be transformed correctly.